Method of laying concrete pavements



- Patented Mar. 12 1929.

UNITED STATES 'IPERGY A. HIPPLE, 0F ATLANTA,'GECRGIA. I

METHOD OF LAYING CONCRETE PAVEMENTS.

No Drawing.

This invention relates to an improved process of producing concrete pavement slabs and particularly to the process of finishing the wear surface of such slabs.

Primarily, the invention seeks to produce a concrete paving slab having a surface of high wear resistant properties, such surfaceof the finished slab being of a substantially nonporous character, due to the fact that pores Agitation effected by thecompacting and finishing of the slab having ceased, the retained water is slowly released by the settling of the finer particles in the concrete mass, these fine particles coming to rest one against the other and having a tendency to free the water and force it to the surface of the slab. When enough water is released fromthe lower portion of the slab to saturate the upper portion of the concrete mass, a surface tension is created and all the remaining surplus Water is quickly drawn to the surface, This accounts for the water sheen or water film on concrete surfaces, which may be observed immediately before the initial setting of the cement. However, the water sheen is dissipated rather quickly by evaporation until the surface tension is broken, at which time the remaining moisture on the surface is drawn by capillary attraction back into the interior of the slab and immediately thereafter the initial setting of the cement begins.

In the production of the slabs, the close interrelation of the aggregate particles is essential to the production of a slab of desired strength, and this association of said particles is effected by the various means which are used for leveling the concrete mass to the desired contour and elevation. The various finishing processes utilized in connection with the production of the slabs all also tend to work the concrete into a compact mass, so as to better effect this close association of the particles which is dependent upon the removal of the Application filed October 7. 1927,- S'erial No. 224,773.

water and entrapped air in the concrete mass. The appearance of the water film at the surface of the concrete slab, as previously mentioned, not only prevents this interlocking and settling together of the fine cement particles at the surface in the manner in which such particles become associated lower down in the structure and which is necessary to the attainment of maximum density and strength, but, on the contrary, the water coming to the surface of the slab actually forces the particles at the surface upward and apart, thereby creat ng pores and capillaries in the act of passlng outward. As a result, the subsequent quick dissipation of the water film or sheen leaves the surface of the finished concrete slab n a disturbed porous state, much below the natural strength developed by the material under ideal conditions.

The porosity of the surface of the concrete pavements laid as above described, causes such pavements to be highly absorbent of moisture and subject to constant expansion stresses, a disturbing factor in all present day concrete paving construction. Furthermore, the disturbed porous state of the cement partlcles near the surface decreases the strength and resistance of such surface against the wear and tear of traffic and other agencies of destruction.

In order to prevent the formation of a wear surface of such porous characteristics, the present invention contemplates a method of finishing the surface of a concrete pavement slab wherein the pores produced on the surface during the accumulation of the water at such surface will be filled with finely divided particles of some suitable substance which does not have any detrimental effect on the slab. More specifically. this finishing process consists in directing a fluid spray against the surface of the slab, whereby solid particles present in the water covered surface will be forcibly driven into the pores in the slab surface. In carrying out the present method, the finely divided solid particles may be in the form of the cement particles which areforced concrete may be used or air may be utilized, it only being necessary that a spray of sufficient force be applied to the surface being finished,

so as to force into thepores the cement par-i ticles in the water sheen or the cement particles or other solids previously applied to the surface. It will be understood, of course, that the spray used is ver fine and the amount of liquid used is not su cient to in any way damage the surface of the cement by washing out any of the cement or fine sand.

Specimens of concrete slabs have been pro duced in accordance with the present invention, as follows: A batch of concrete in proportion 1 part cement, 2 parts sand and 4 parts washed gravel (a mixture which is the standard for highwaypavements laid down by the Federal Bureau of Roads) was placed in forms, compacted and finished as nearly as possible in the manner in which the average pavement slab is finished today. After wa- 'ter, which was forced out in the process of finand that the spray had no further effect on the cement surface, the spray was discontinued and the specimen considered finished. Where additional cement partlcles or other solids were applied to the surface of the slab,

the concrete mix was placed in aform and preliminarily finished, as described in the previous example. However, immediately upon the appearance of the water sheen or film, the surface of the slab was subjected to a blast of neat cement delivered from above by means of an instrument similar to a sand blaster. It could be observed that this cement blast was closing the pores created in the sur- J face of the slab, by the upward movement of the water sheen; and such cement blast could be plainly seen to exert a settling influence on the wet surface. The cement spray was continued until the surface was apparently uniformly or evenly coated with neat cement, whereupon the water spray described in the preceding example was immediately applied. The water spray was continued until it was apparent to the naked eye that all the pores were closed and all of the superficially applied neat cement tightly packed. At this time the water spray would have no further effect on the cement surface, so that the spray was discontinued and the slab considered finished.

While water has been specifically mentioned in the examples given, it isv believed thatin lieu thereof any liquid not chemically deterrent to the setting of the cement may be used for the spray and would effectively achieve objects sought by the present invention. Instead of a liquid, an air blast alone would probably suflice, as any agency that 'Wlll agitate the concrete surface at the time to drive such free particles into the pores formed in the slab. Y

Slabs produced in accordance with the present invention have been found by actual tests to have exceedingly high wearing properties. A sample of a slab made in accordance with the ordinary practices of today; a second'slab made by the use of the Water spray alone; and a third slab made by the use of the superficially applied neat cement and Water spray were all furnished to one of the State schools of technology at whose highway material laboratory the same were subjected to wear tests. For the purposes of these tests the surfaces of the several blocks were ground wlth carborundum stones, corresponding to about *two years wear on a medium trafiic street. Below is given a table showing the cubic inches Worn off per square foot of sur face and the wear in per cent of a 6 inch pavement. .As the three specimens appear in the table in the order in which they are above listed, it will be observed that both of the samples made in accordance with the present I invention possessed much higher wearing properties than the ordinary slab, the slab made by the use of superficially applied cement and water spray possessing wearing qualities about six times as great as the ordinary slab.

Speci- Speci- Specimen 1. men 2. men 3.

Cu. inches worn ofl per sq. ft. of surface 6. 95 1.87 1. 15 L Wear in per cent of a 6' pavement 0. 7% 0. 22% 0.13%

What I claim is:

1. The process of producing concrete pavement slabs which consists in permitting water used in the concrete mass to hydrate the cement to accumulate in film like form on the surface of said slab and subsequently forcing particles of cement carried in said water film into pores formed in said surface during-the accumulation of said water film by means of a fluid spray such as water.

/ 2. The process of finishing the wear surfaces of concrete slabs, which consists in directing a blast of fluid against said surface to forcibly introduce free solid particles into pores formed in said surfaces by exuding water initially used in the concrete mix for hydrating the cement therein.

3. The process of finishing the wear surfaces of concrete slabs, which consists in permitting the formation of a water sheen or film on the surface of the slab, then applying a coating of finely divided solids to the slab surface, and finally forcing the solids into pores formed in said surface during the formation of said water sheen by a fluid spray of extreme fineness and of a volume insuflicient to Wash the solids out of the pores.

4. The process of finishing the wearing surface of a concrete slab which consists in permitting the accumulation of a water sheen or film on said surface, then depositingifinely divided particles of a solid on said surface, and then spraying said surface with a fluid to force said particles in pores formed in said surface during the accumulation of said water sheen, said spray being of a fineness and film on said surface, then depositing fineparticles of neat cement on said surface,,and

finally spraying said surface with water to M force the neat cement into pores formed in said surface during accumulatlon of said water sheen, said spray being of a degree of fineness and of a volume insuflicient towash the neat cement from the pores.

6. The step in finishing concrete pavement slabs which consist in forcibly introducing fine particles of cement into the pores formed in the surface of said slabs by the rising w'ater mixed with the mass of concrete for hydration of the cement therein, by directing against the surface of the pavement slab a fine spray of a fluid not chemically deterrent to the setting of the concrete. 4

- PERCY A. HIPPLE. 

